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[D-4.2.2 Nutrients Condition of Coastal Waters]

[Contact Person]

Matsukawa Yasuo
Section Director
Marine Biotic Production Division
National Research Institute of Fisheries Science
Fisheries Agency
2-12-4 Fukuura, Kanazawa, Yokohama 236, Japan
Tel:045-788-7651, Fax:045-788-5001
E-mail:matsuyan@nrifs.affrc.go.jp

[Total Budget for FY1994-1996]

9,226,000 Yen (FY1996 3,091,000 Yen)

[Abstract]

　In order to find out the criterion to protect coral reef ecosystems at Ryukyu Islands from eutrophication due to developments, nutrient concentrations in reef waters and vegetative density of corals were investigated. DIN ranged from 10^-1μM to 10⁰μM and DIP from 10^-2μM to 10^-1μM, corresponding to a higher level of nutrient concentrations in tropical reefs. Corals tended to decline or give place to sargassum or zostella with progress of eutrophication or siltation. The relationship between nurient concentrations and vagetative density suggested, on the whole, that the standard of water quality in reefs for protection of corals should be established at a level of 10⁰μM in DIN and 10^-1μM in DIP. Nucleic acid ratio(RNA/DNA) and carbon stable isotope ratio(δ¹³C) in corals were also monitored as indexes of physiological condition of corals. The observed characteristics of ratios suggested that RNA/DNA could be an index of growth and maturation potential and that the difference of δ¹³C between zooxantella and coral tissue could be an index relating to symbiosis, that is, dependence of corals on photosynthetic product of zooxantella. These results should be confirmed with further observations and experiments.

[Key Words]

Coral reef environment, Nutrients concentration, Nucleic acid ratio, Carbon stable isotope, Ryukyu Islands